The present invention relates generally to the fabrication of lightweight structural elements and more particularly concerns a method of welding hollow elongated beams.
In the fabrication of large load supporting and lifting devices such as heavy duty cranes and the like, it is desirable to utilize components which have high strength to weight ratios. Generally, these requirements are best met by hollow tubular members of substantial depth and width relative to their wall thickness. The fabrication of large elements of the foregoing nature, in the past has been both difficult and costly. Hollow steel members of substantial cross-section cannot be directly formed at steel rolling mills except with the installation of very expensive equipment which must be altered for each different cross-section to be formed. This makes the per unit cost of such hollow members essentially prohibitive.
Post forming of large size hollow elongated members such as by welding also has been generally unacceptable due to warpage and deflections induced or created during fabrication of the members. The prior art has, of course, recognized some of the problems which occur during welding beams, frames and other structural elements and certain solutions to these problems have been suggested. Nilsson et al. U.S. Pat. No. 3,199,174, for example, suggests uniformly heating the web of an I-beam while the flanges are welded to the web to prevent cross-sectional sagging of the web during cooling. Seedorff et al. U.S. Pat. No. 3,516,147 teaches simultaneously spot-welding the corners of a lightweight metal frame to insure cross-sectional accuracy. Yancey U.S. Pat. No. 3,882,654 teaches the use of an angle reinforcing bar welded into the corner of two abutted plates to prevent welding "blow-through" and to reduce stress concentrations at the corner. However, none of these references deal with the problem of longitudinal warpage and deflection of hollow elongated beams during fabrication by welding.